1. Field of the Invention
The present invention relates generally to inkjet printers and, in particular, to wiping the printheads of one or more print cartridges of an inkjet printer. Most particularly, the invention relates to method and structure that depend upon printer carriage motion for automatic, uni-directional, separate wiping of each printhead utilizing an integrated removable wiper structure.
2. Related Art
Inkjet printhead nozzles commonly become plugged with ink blobs or particulate, or otherwise contaminated with internal bubbles that prevent the nozzles from operating properly, resulting in lower print quality. Consequently, inkjet printers typically include a service station that provides for spitting, wiping, capping and priming of single printheads in order to keep the printhead nozzles clean and functioning.
Conventional service stations frequently require operator intervention and often take the printer off-line for several seconds. It is desirable to automate printhead servicing to free the operator for other tasks, and to perform servicing as quickly as possible.
Failure recovery methods and systems have been proposed that provide for the automatic recovery from a condition in a plural printhead inkjet printer in which the printhead's nozzles become clogged with ink and particulate, wherein the method includes capping the printheads, selectively priming and flushing a given printhead and then uncapping and wiping the printheads. One such method and system is described in commonly owned, copending U.S. patent application Ser. No. 07/949,318, entitled "Automatic Failure Recovery for Ink-jet Printheads," filed on Sep. 21, 1992, the disclosure of which is incorporated herein by reference.
Wiping in conventional service stations is typically done with a single wiper that wipes the printhead in each of two directions. This is undesirable because wiping an inkjet printhead in two directions results in recontamination of a printhead during wiping, and wiping multiple printheads with a single wiper surface results in inter-printhead contamination.
Previously, wiper blades have been mounted below a surface of a movable sled and extended through a hole in the surface. Consequently, the wiper blades have been relatively long and, therefore, not as stiff as desired. Generally, it is desirable to make the wiper blades as stiff as possible, without damaging the printhead, so that the most effective wiping will be obtained.
Additionally, the angle at which the wiper blade wipes across the printhead ("wiper blade angle of attack") has been found to be an important factor in effective wiping of the printhead. Generally, the most effective wiping is obtained when the wiper blade angle of attack is as close as possible to 90.degree..
Previously, wiper blades have been made of rubber. A rubber wiper blade bends as the wiper blade comes into contact with the print cartridge. The amount of bending, i.e., the amount by which the wiper blade angle of attack deviates from the desired 90.degree. angle, depends upon the amount of interference between the wiper blade and the print cartridge. In previous service stations, cumulation of tolerances associated with the nominal positions of the service station sled (on which the wiper blades are mounted) and the print cartridge printheads necessitate a large nominal interference between the wiper blades and the printheads in order to ensure contact between the wiper blades and the printheads during wiping. This large interference results in a wiper blade angle of attack that is typically less than 30.degree. when rubber wiper blades are used. Thus, rubber wiper blades do not wipe as well as desired.
Further, with rubber wiper blades, "shingling" of the wiper blades can result after prolonged used of the wiper blades, particularly in low humidity and low temperature environments. Shingling is a microscopic defect on the surface of the wiper blade that, during wiping, can cause air bubbles to be transmitted into the nozzles of the print cartridge. These air bubbles can cause ink to be displaced from the firing chamber of the print cartridge so that the print cartridges will not print, necessitating priming of the print cartridge in order to restore printing capability.
In order to achieve good wiping, it is necessary to maintain a minimum wiping force between the wiper blades and the printheads. It is also desirable that the wiping force remain approximately constant despite variations in the amount of interference between the wiper blades and the printhead. Further, the wiper blades must maintain contact with the printhead along the entire length of the wiper blade to achieve the best wiping. Thus, the wiper blade must be supported by a structure that accomplishes these functions.
Print cartridges containing a pigmented ink, e.g., a black pigmented ink, are particularly difficult to wipe effectively, as compared to print cartridges containing a dye. Thus, the above-noted characteristics of a good wiper blade, e.g., stiffness, wiper blade angle of attack near 90.degree. and adequate wiping force, are particularly important for wiper blades that wipe printheads of print cartridges that dispense pigmented ink.
Because of the frequent contact between the wiper blades and the print cartridge, the wiper blades wear out quicker than the remainder of the service station, e.g., the capping mechanism and the service station sled. Consequently, it is desirable that a user be able to replace the wiper blades or wiping structure without the necessity of replacing the remainder of the service station.